I didn't look in the book but I dont see how Dual Rate would help you.

Put the 3 position switch in the center and rig the flaps for half down.

Set the flap channel end points to 0.

Flip the switch up and raise the end point till the flap stops where you want it to.

Flip the switch down and raise the end point till the flap stops where you want it to.

If up switch = down flap and you want it the other way reverse the flap channel in the reverse menu.

Fly and enjoy.